The invention relates generally to water pumps and more specifically to water pumps having an electrically controlled viscous coupling drive.
Water pumps are typically used on vehicles today to provide heat transfer means for an engine during operation. The engine crankshaft typically drives water pumps at a fixed ratio. Thus, as the engine idle speed is reduced, as is the trend in vehicles today to reduce emissions, the water pump speed is correspondingly reduced. This reduction in water pump speed results in a reduction in the coolant flow through the cooling system which can result in poor heater output for the interior of the vehicle when needed in cold weather and also can result in poor coolant flow for engine cooling during hot weather.
Increasing the water pump speed by increasing the drive ratio from the crankshaft will increase the coolant flow at engine idle speeds, but it may result in overspeeding the pump at higher engine speeds which may produce pump cavitation and reduced water pump bearing life. Pump cavitation can result in pump damage and a reduction in cooling system performance.
The current state of the art is to add an auxiliary water pump, typically electrically driven, to provide additional coolant flow at low engine idle speeds. Another approach is to use moveable vanes in the inlet of the water pump to throttle the coolant flow at higher engine speeds.
It is thus an object of the present invention to provide good coolant flow at low engine idle speeds while avoiding pump cavitation at higher engine speeds without the need for an auxiliary water pump or moveable vanes. It is another object of the present invention to control the speed of the water pump for improving emissions and fuel economy.
The above and other objects of the invention are met by the present invention that is an improvement over known water pumps.
The present invention provides a clutch arrangement that uses two disks that are coaxial, normally in close proximity, and contain a viscous fluid, typically silicon fluid, on all sides and in the small space (shear gap) between them. The input disk is driven at water pump pulley speed. The driven disk is separately mounted on a shaft connected to the water pump impeller and is capable of being flexed at the center (hub area). By flexing the disk away from the input disk, the shear gap can be increased and the torque transmission decreased, thereby turning the impeller at a slower speed. An electromagnet provides the force to flex the driven disk. By controlling the amount of electric energy provided to the electromagnet, and hence the flex in the driven disk, the impeller speed can be precisely controlled.
The electronically controlled viscous coupling thus provides good coolant flow at low engine idle speeds while avoiding pump cavitation at higher engine speeds without the need for an auxiliary water pump or moveable vanes. This also improves fuel economy and emissions by maintaining the engine within an acceptable temperature range at regardless of engine speed.
Other features, benefits and advantages of the present invention will become apparent from the following description of the invention, when viewed in accordance with the attached drawings and appended claims.